WordPress instance is broken: Decoding failed: Syntax error

Symptoms

• WordPress instance is shown as broken in Domains > example.com > WordPress with the following error in Plesk interface:

  PLESK_ERROR: Decoding failed: Syntax error

• The error like below is displayed in Plesk logs %plesk_dir%admin\logs\php_error.log:

  CONFIG_TEXT: [extension/wp-toolkit] [5b14f2b719fd6] Starting: D:\Plesk\Additional\PleskPHP56\php.exe -dsafe_mode=off -ddisplay_errors=off -dopen_basedir= D:\Plesk\Additional\modules\wp-toolkit\vendor\wp-cli\wp-cli\php\boot-fs.php "--path=D:\vhosts\example.com\httpdocs" admin-username check-password "" ""
  [extension/wp-toolkit] [5b14f2b719fd6] Finished, Error code: 20101, stdout: , stderr: Administrator with '' username was not found.
  {"err_code":20101,"err_message":"Administrator with '' username was not found."}

• With enabled debug logging the following may be seen:

  CONFIG_TEXT: [extension/wp-toolkit] An error has occurred when decoding JSON by Zend_Json: Illegal Token
  DEBUG [extension/wp-toolkit] An error has occurred when decoding JSON by Zend_Json: Illegal Token
  Trace: #0 C:\Program Files (x86)\Parallels\Plesk\admin\plib\vendor\plesk\zendframework\library\Zend\Json\Decoder.php(113): Zend_Json_Decoder->_getNextToken()
  ERR [extension/wp-toolkit] Unable to fetch WordPress multisite flag for WordPress instance #1 ('') Reason: An error has occurred when decoding JSON returned by wp-cli: 'Illegal Token'

Cause

There are BOM symbols in %plesk_vhosts%example.com\httpdocs\wp-includes\functions.php file, which prevents correct functionality of Wordpress instance in WordPress ToolKit.

The issue is submitted as bug #EXTWPTOOLK-1583, which is planned to be fixed in one of the future Plesk updates.

Resolution

Until the fix is available use the following workaround:

1. Log into the server via RDP;

2. Download the attachment with the script which converts BOM symbols into UTF-8 and unpack it in C:/;

3. Open Command Prompt as Administrator and execute the following command, replacing example.com with the name of the domain where issue exists:

   C:\> php.exe "C:\check_utf8.php" "%plesk_vhosts%example.com\httpdocs\"